Polycarbonate polyols are known to have utility as building blocks for the construction of co-polymers such as flexible urethane foams, urethane coatings, rigid urethane foams, urethane/urea elastomers and plastics, adhesives, polymeric coatings and surfactants among others. Existing commercial polycarbonate polyols fall into two classes, those with perfectly alternating structure in which each repeating unit in the polymer chain contains a carbonate linkage, and those containing a mixture of carbonate and ether linkages (more properly called polyether polycarbonates). The former are derived from diols such as 1,4 butane diol or 1,6 hexane diol and phosgene (or its equivalent) and have three or more CH2 groups between each carbonate linkage, while the latter have a two carbon chain between each carbonate linkage and are typically made from epoxides and CO2 using double metal cyanide catalysts. Polyols with two carbon atoms separating the carbonate linkages and having a perfectly alternating structure are not available commercially. Polyols derived from epoxides and CO2 and having a perfectly alternating structure have only recently been made and are described in WO 2010/028362. Examples of such polyols include poly(propylene carbonate) (PPC); poly(ethylene carbonate) (PEC); poly(butylene carbonate) (PBC); and poly(cyclohexene carbonate) (PCHC) as well as copolymers of two or more of these.
To have utility in these applications, it is preferable that all polycarbonate polymer chain ends terminate with hydroxyl groups. Such hydroxyl groups serve as reactive moieties for cross-linking reactions or act as sites on which other blocks of a co-polymer can be constructed. It is problematic if a portion of the chain ends on the APC are not hydroxy groups since this results in incomplete cross-linking or termination of the block copolymer. A typical specification for aliphatic polycarbonate polyol resins for use in such applications is that at least 98% or in some cases greater than 99% of chain ends terminate in hydroxyl groups. In addition, these applications typically call for relatively low molecular weight oligomers (e.g. polymers having average molecular weight numbers (Mn) between about 500 and about 15,000 g/mol). It is also desirable that the polyols have a narrowly defined molecular weight distribution—for example, a polydispersity index less than about 2 is desirable, but much narrower distributions (i.e. PDI<1.2) can be advantageous. Furthermore, for certain applications, polyol polycarbonates having little or no contamination with ether linkages are desirable. Although progress has been made recently employing particular catalysts along with chain transfer agents, new advances in producing polycarbonate polyols having a high percentage of —OH end groups are needed.